In recent years, various techniques for crystallizing or improving the crystallinity of an amorphous or polycrystalline semiconductor film have been investigated. Such crystallized thin films may be used in the manufacture of a variety of devices, such as image sensors and active-matrix liquid-crystal display (“AMLCD”) devices. In the latter, a regular array of thin-film transistors (“TFTs”) is fabricated on an appropriate transparent substrate, and each transistor serves as a pixel controller.
Prior art methods for improving the crystallinity of the semiconductor film typically involve irradiating the thin film with a shaped laser beam. The shaped laser beam optimally should be a long line beam with a uniform width, a top-hat short axis profile, and uniform energy along its length. However, producing such a beam is challenging and most line-beams will have non-uniformities along the length of the beam, while the cross-section of the beam is more rounded or, in some instances, Gaussian. The non-uniformities can have random and periodic components (hereinafter referred to as “random non-uniformities” and “periodic non-uniformities”, respectively). These non-uniformities in the laser beam can translate to non-uniformities in the film, which results in non-uniformities in the devices implementing the films, for example, non-uniformities in the brightness of a display in a AMLCD application.